Common Platelet-Poor Plasma Validation Errors and How to Prevent Them

Platelet-poor plasma (PPP) validation can fail even when a centrifuge is working properly. When residual platelet counts come back above the acceptable limit, it can be difficult to know whether the problem is the centrifuge, the cycle settings, sample handling, or the way the platelet count was measured.

When a PPP validation fails, start by confirming that the centrifuge is operating correctly. If the equipment checks out, review sample handling. Refrigerated specimens, aspiration near the buffy coat, and aggressive pipetting are easy to overlook and should be investigated before changing the validated centrifugation protocol.

What Is Platelet-Poor Plasma?

Platelet-poor plasma is generally defined as plasma containing fewer than 10 × 10³ platelets/µL. Residual platelets can affect some coagulation testing, including lupus anticoagulant testing and certain frozen heparin samples, so the required preparation depends on the intended assay.¹

For clinical laboratories performing PPP validation, the goal is not simply to achieve a particular RPM or run time. The complete centrifugation and handling process needs to produce plasma that meets the requirements for the intended application.

Ensure Room Temperature Samples Before Centrifugation

If residual platelet counts are unexpectedly high, check whether samples were chilled before or during centrifugation. The International Council for Standardization in Haematology (ICSH) recommends maintaining citrated blood samples at 18–24°C during transport, storage, and centrifugation.¹,⁷

Lower temperatures increase whole-blood viscosity, which could affect platelet sedimentation during centrifugation and potentially leave more residual platelets in the plasma.⁶ Cold exposure can also cause precipitation or activation of certain clotting factors, affecting coagulation test results.¹,⁷

If samples were refrigerated before centrifugation, repeat the preparation using freshly collected specimens maintained at 18–24°C.

Don’t Aspirate Too Close to the Buffy Coat

Sample handling can have a significant effect on PPP results, even when centrifugation was performed correctly. In the 2026 study by Drucker Diagnostics, plasma was transferred from the upper portion of the sample while leaving the lower layer undisturbed. The study found that aspirating essentially all of the plasma down to the buffy coat increased residual platelet counts.²

When transferring plasma after centrifugation, avoid disturbing the layers. If a validation result is unexpectedly high, repeat the transfer carefully before changing centrifuge settings.

Avoid Aggressive Pipetting After Centrifugation

Pipetting technique can also contribute to PPP validation failures. The report by Drucker Diagnostics found that repeatedly pipetting plasma up and down increased residual platelet counts and produced the largest increase among the handling variations evaluated.² The study’s standard procedure used a single gentle aspiration of the upper portion of the plasma.

Unnecessary agitation during plasma transfer can introduce additional variability into the result. When investigating elevated residual platelet counts, ensure that plasma is transferred gently using proper technique and without repeated pipetting. One way to identify potential handling inconsistencies is to have another technologist independently repeat the preparation using the same protocol. Differences in residual platelet counts may help identify variations in technique.

Confirm the Residual Platelet Count

If the result is close to the acceptance limit, the platelet-count method itself should also be considered.

Low platelet counts can have variable precision depending on the analyzer method.⁴ Review the analyzer method and reportable range, particularly when results are near the acceptance threshold. When possible, use the same platelet-count method for repeat validation so that the results can be compared consistently.

If the centrifuge and sample preparation appear to be performing as expected, confirming the measurement method can help determine whether the difference is related to the sample preparation or the analysis.

Match PPP Preparation to the Test

There is not one universal PPP preparation that is appropriate for every coagulation application. The required preparation can differ between fresh routine testing, frozen samples, and other specialized applications.¹ Some workflows may specify additional centrifugation, but a second spin is not automatically better.

Use the plasma preparation specified for the intended assay rather than adding centrifugation steps simply because a validation result was unexpected. Changing the preparation can introduce another variable without addressing the actual cause of the failure.

Confirm Centrifuge Performance and Settings

Regardless of the suspected cause, the first step when troubleshooting a failed PPP validation is to confirm that the centrifuge is performing as expected. Check the programmed speed and cycle time, along with the rotor condition, service and calibration records, vibration, and any error messages. Confirm that the centrifuge is reaching the required speed and completing the full cycle.

It is also important to verify RCF rather than relying on RPM alone. The rotor radius affects the centrifugal force applied to the sample, so the same RPM can produce different RCF values on different centrifuges or rotors.

Confirm the xg value on the actual rotor being used. Do not assume that an RPM setting from another centrifuge produces the same result.

Rotor design can also affect plasma separation. Fixed-angle and horizontal rotors produce different sedimentation patterns, which can influence residual platelet counts and the potential for remixing after centrifugation. When changing rotor configurations, verify that the established RCF and run time still produce acceptable PPP.¹

RCF and Time Work Together

RCF and run time should be considered together when validating a PPP protocol. A lower force applied for a longer period is not automatically equivalent to a higher force applied for a shorter period.

A 2026 Drucker Diagnostics study evaluated centrifugation and handling variables that can affect PPP preparation. In the study, 4,400 xg for 2 minutes produced the lowest mean residual platelet count among the tested DASH Coag settings, while 2,700 xg for 5 minutes left the most residual platelets. All of the tested DASH Coag settings met the study’s PPP criteria, but the results showed that RCF had a greater influence on residual platelet counts than time under the conditions evaluated.²

If the centrifuge itself checks out, validate the complete cycle on the actual centrifuge and rotor before changing other parts of the PPP protocol.

Use the Validated Brake Setting

Brake settings sometimes become a focus when a PPP validation fails, but the brake should not be evaluated in isolation. In the Drucker Diagnostics study, different brake levels on the DASH Flex 12 did not have a meaningful effect on final platelet counts under the conditions tested. PPP was achieved consistently across the tested deceleration profiles.²

A separate 2026 study evaluating centrifuge braking for hemostasis testing also found that the effect of braking depended on the overall centrifugation protocol rather than the brake setting alone.³

When in doubt, always use the brake setting that has been validated for the specific centrifuge, RCF, run time, rotor, and workflow. Do not assume that brake-on or brake-off will produce better PPP without validating the complete protocol.

How Often Should PPP Be Verified?

PPP verification should be part of a lab’s ongoing equipment and process management. The International Council for Standardization in Haematology recommends checking residual platelet counts before introducing a new centrifuge and every 6–12 months.¹ Verification should also be repeated after relevant centrifuge repair or recalibration when the change could affect performance.

CLSI H21 calls for residual platelet counts to be verified at least annually and after a change to the centrifuge.⁵ Following your laboratory’s applicable requirements and established validation procedures helps ensure that the centrifuge and PPP preparation process continue to perform as expected.

A Failed Validation Doesn’t Always Mean a New Centrifuge Is Needed

When a PPP validation fails, it can be tempting to immediately focus on the centrifuge. Taking the time to work through each part of the process can help identify the source of a failed validation without changing multiple variables at once.

Once the cause is identified, make the appropriate adjustment and repeat the validation to confirm that the process is performing as expected.

Troubleshooting a Failed PPP Validation Checklist

If residual platelet counts exceed the acceptable limit:

• Check centrifuge performance. Confirm the centrifuge reaches the required speed, completes the programmed cycle, and has no indications of malfunction.
• Verify the centrifugation protocol. Confirm RCF, run time, rotor configuration, and brake settings match the validated procedure.
• Review recent equipment changes. Determine whether repairs, recalibration, or rotor changes could have affected separation performance. Include the analyzer used to measure platelet counts.
• Check sample temperature. Confirm specimens were maintained at the recommended 18–24°C before and during centrifugation.
• Review sample handling. Confirm proper pipetting technique. Have another technologist independently repeat the preparation using the same protocol to help identify technique-related variability.
• Repeat verification. After correcting an identified problem, repeat the appropriate testing to confirm acceptable residual platelet counts.

References

1. Kitchen S, Adcock DM, Dauer R, et al. “International Council for Standardization in Haematology recommendations for processing of blood samples for coagulation testing.” International Journal of Laboratory Hematology. 2021;43(6):1272–1283. doi:10.1111/ijlh.13702.
2. Jordan K. Evaluation of Centrifugation and Handling Variables in Platelet-Poor Plasma (PPP) Preparation. Drucker Diagnostics. March 2026.
3. Jury V, Talon L, Tourret E, Lebreton A, Sinegre T. “Impact of Centrifuge Braking on Platelet-Poor Plasma for Hemostasis Testing.” International Journal of Laboratory Hematology. 2026;48(1):179–187. doi:10.1111/ijlh.14554.
4. Schoorl M, et al. Study on platelet-count methodology and precision at low platelet concentrations. 2013.
5. Clinical and Laboratory Standards Institute. H21: Collection, Transport, and Processing of Blood Specimens for Testing Plasma-Based Coagulation Assays. 6th ed. 2024. CLSI H21.
6. Neumann FJ, Schmid-Schönbein H, Malotta H. Effect of temperature dependent changes in mechanical stability of red cell aggregates on relative apparent whole blood viscosity. Biorheology. 1987;24(5):463–472. https://doi.org/10.3233/BIR-1987-24504
7. Adcock DM, Moore GW, Kershaw GW, Montalvao SAL, Gosselin RC. International Council for Standardization in Haematology recommendations for the performance and interpretation of activated partial thromboplastin time and prothrombin time mixing tests. Int J Lab Hematol. 2024;46(5):777–788. https://doi.org/10.1111/ijlh.14344